Single pipe pile is widely applied to the architecture engineering due to its high load-bearing capacity, well-adaptability to geological conditions having biggish varieties of the geological supporting layer, low cost, and fast construction. End plates of pipe pile are disposed at both ends of pipe pile and are the annular disk members made of metal. The end plates are mainly configured to stretch a reinforcement cage, and make the reinforcement cage generate a prestress during manufacturing process, while the end plate will be suffered from hit of the pile driver during pile-sinking process. Two adjacent pipe piles can be coupled firmly by the end plates. Generally, two prestressed concrete piles are coupled with each other by welding their couplings, for example, their end of plates, on site. However, the welding requires long time, namely approximate 30 minutes per coupling. Moreover, the welding quality will depend on the skill of worker. Sometimes the piles are driven into the earth immediately after the welding, the welding flaw will therefore unable to be found. A quenching cracking or water embrittlement on the couplings may occur when the couplings were driven into the earth and the couplings may therefore be damaged easily when they suffered the bias pressure due to varied geological conditions. In sampling test for the piles foundation, some unfirm or uncompleted welding have been found and caused that the capacities of bearing pressure, anti-bending, anti-shearing and resistant extraction at the coupling do not meet the designed requirement, and therefore supplementary welding is needed which wastes materials and delays the work process. Furthermore, when the coupling is being welded, its surface has a high temperature, thus an advanced antiseptic treatment for the coupling cannot be carried out, and the quality and lifetime of the coupling will be unsure.
A number of mechanical couplings used for pipe pile mainly comprise mechanical engagement coupling, mechanical flange coupling, mechanical fastening coupling and mechanical screw coupling, but there are certain flaws among them. For example, the mechanical engagement coupling has a complicated structure and high costs, in which a built-in clamping spring may easily be corroded and aged so that the spring loses its elastic property; The mechanical flange coupling, fastening coupling and screwed coupling all have an enlarged member, which virtually increase a resistance for the pile driving, and their coupling intensity may need to be improved.